The present invention relates to lasers and especially to a laser having multiple pulse duration and pulse rate modes of operation.
The laser resonator considered has a solid state laser gain medium mounted between resonator end reflectors and has optical switching elements located therein. The laser resonator provides two distinct modes of operation, conventional Q-switched operation, with pulse width equal to several cavity round-trip times, and Q-switched cavity dumped operation, with pulse width equal to approximately one cavity round-trip time. The pumping source is controlled along with the switching techniques to provide a single laser operable in two distinct modes at widely varying pulse rates and excellent efficiency.
Prior U.S. patents of interest may be seen in the Uchida et al. U.S. Pat. No. 5,740,194 for a solid state laser apparatus in which a Nd:YAG laser varies the number of pumping LED""s to adjust the pulse width time and spacing. This patent controls relatively long pulse lasers by varying the pumping characteristics and time to change the output and does not change the dynamics of the laser pulse buildup and would not be effective in very short duration ranges typical of Q-switched pulses. The U.S. Patent to Holleman et al. U.S. Pat. No. 5,721,749 provides a laser pulse profile control by modulating relaxation oscillations and controls the timing and form of pulses of a solid state laser with an acousto-optic modulator. By varying the duty cycles of laser diodes, the internal dynamics of a multi-pulsed relaxation oscillator is used to obtain desired characteristics of amplitude and pulse duration. This patent relies on relaxation oscillations and works with gain switched pulses rather than Q-switched pulses. There is no capability for achieving very short pulses. The Injeyan et al. patent, U.S. Pat. No. 5,488,619, is a Q-switched micro-laser having an array of individual intracavity Q-switches and uses multiple parallel lasers to generate small pulses which may be combined to form a generally incoherently single output beam. The Emmons, Jr. et al. patent, U.S. Pat. No. 5,197,074, is for a laser system with multi-function intraresonator loss modulation to form output pulses of selectible duration and controls the relative amplitudes of pulses within a multi-pulse range. The Bille et al. patent, U.S. Pat. No. 4,764,930, is a multi-wavelength laser source which provides a plurality of pulsed laser beams using a plurality of LED""s and uses a complex mode locked laser and grating or prism pulse compressor to generate short pulses. The Wayne et al. patent, U.S. Pat. No. 4,528,668, is a programmable multifunction laser which selectively uses Q-switch pulses and cavity dumped pulses as a means to achieve pulses of significantly different temporal width. It does not use controlled pump-pulse duration to control the stored energy in the gain medium at the time of Q-switching, as in the present invention. It also does not have the ability to either Q-switch conventionally or to allow Q-switching to occur with no out coupling followed by rapid cavity dumping when used in conjunction with control of the pulse duration to select pulse energy pulse rate and pulse duration over relatively broad ranges and with a high laser efficiency. This patent relates to gas lasers rather than the solid state lasers of the present invention. The Wayne et al. patent, U.S. Pat. No. 4,176,327, is a method for cavity dumping a Q-switched laser with varying pulse frequency of a gas laser. It is similar to the Wayne et al. ""668 patent. The Fountain et al. patent, U.S. Pat. No. 4,019,156, is for a dual Q-switch Nd:YAG laser with active and passive Q-switches to produce dual modulation for differing pulse durations. The combination passive-active mode locked configuration provides some control over pulse widths but in a range which is much shorter than in the present invention. The Iliff patent, U.S. Pat. No. 3,970,967, is for a ultrafast light shutter utilizing two sets of Pockels cell polarizer combinations to select laser pulse duration and does not deal with the control of laser dynamics, as in the present invention. The Landry patent, U.S. Pat. No. 3,699,474, is for a multiple beam laser obtained by sequential Q-switches. Spatially separated laser outputs are derived from a single laser gain medium leading to independent incoherent outputs. The Sooy patent, U.S. Pat. No. 3,521,188, is a double Q-switched laser with self-mode locked intracavity loss module which will generate short pulses but which does not provide true multi-function control of the dynamics of the laser to achieve different pulse durations and energies. One Q-switch holds back oscillation in the cavity until pumped to a higher inverted state and a second Q-switch operates to switch out of the cavity a single pulse. The Boyden patent, U.S. Pat. No. 3,423,695, is for a dual Q-switched laser having one active and one passive Q-switch to generate an output pulse and to clean up and improve the timing jitter of a laser output pulse.
The present invention uses intracavity laser dynamics in a laser resonator to achieve two distinct modes of operation including a conventional Q-switched operation with a predetermined pulse width and a Q-switched cavity dumped operation with a different pulse width controlling the pumping source and employing switching techniques to allow a single laser to produce efficient, relatively high energy, long duration pulses at short pulse rates, or alternatively, low energy short duration pulses at high pulse rates.
A laser apparatus achieves multiple pulse duration and pulse rate modes of operation using intracavity optical switching it a laser resonator. The laser resonator has a solid state gain medium located between a pair of end reflectors and one or more optical switches. The laser pump uses a pump source which can be varied in pulse duration to allow multiple output pulse rates. The laser has a Q-switched mode for out coupling laser energy from the laser resonator at a constant, predetermined outcoupling fraction in one mode of operation, producing a pulse duration equal to several cavity round-trip times. The laser also has cavity dumping capability for coupling the Q-switched laser energy out of the laser resonator in a second, short pulse mode of operation in which the laser pump is operated to produce a second predetermined pulse rate. No outcoupling is allowed to occur initially in this mode so that a pulse can build rapidly and efficiently extract energy from the gain medium. After essentially all the stored energy is extracted from the laser medium, it is cavity-dumped in approximately one cavity round-trip time. Intracavity optical switching of the laser resonator is used to achieve the two distinct modes of operation: conventional Q-switched operation, with pulse width equivalent to several cavity round trip times; and Q-switched cavity dumped operation, with pulse width equivalent to about one cavity round trip time.